1. Field of the Invention
The present invention relates to a common rail such as a high pressure fuel manifold in an accumulator fuel injection system of a diesel internal combustion engine, a block rail or the like.
2. Description of the Prior Arts
Conventionally, there have been known common rails of this kind, for example, as illustrated by FIGS. 21 and 22. The common rail shown by FIG. 21 is of a system constituted by perforating branch holes 21-2 each having a pressure receiving seat face 21-4 communicating with a flow path 21-1 of a main pipe rail 21 and opened outwardly at a plurality of boss portions 21-3 provided at intervals at a peripheral wall portion in the axial direction on the side of the main pipe rail 21 comprising a circular pipe, engageably bring pressing seat faces 22-3 constituted by connection head portions 22-2 on the side of branch pipes 22 into contact with the pressure receiving seat faces 21-4 on the side of the main pipe rail 21 and screwing fastening box nuts 23 previously integrated to the side of the branch pipes via washers 24 to male screws (outside screws) 21-5 provided on outer peripheral faces of the boss portions 21-3 to thereby fixedly fastening the branch pipes to the main pipe rail by pressing action at the connection head portions 22-2. In FIG. 21, notation 22-1 designates a flow path of the branch pipe 22.
Further, a common rail shown by FIG. 22 is of a system constituted by machining bottomed holes to a plurality of boss portions 21-3 provided at intervals at a peripheral wall portion in the axial direction on the side of a main pipe rail 21 similar to FIG. 21, providing female screws (inside screws) 21-6 on inner peripheral faces of the bottomed holes and screwing fastening male nuts 25 to the female crews (inside screws) 21-6 to thereby fastening branch pipes to the main pipe rail 21 by pressing action at the connection head portions 22-2. Incidentally, in FIG. 22, numeral 26 designates a sleeve washer.
However, in the case of a common rail having a structure where the branch hole 21-2 is installed to the boss portion 21-3 provided to the main pipe rail 21 comprising a circular pipe, large tensile stress is caused at an opening end portion P at the flow path of the main pipe rail in the branch hole 21-2 by high inner pressure of the main pipe rail 21 and cracks are liable to cause with the opening end portion P as onset which may give rise to leakage.